Forced flow vapor generating unit



Nov. 29, 1960 P. H. KOCH 2,962,005

FORCED FLOW VAPOR GENERATING UNIT Filed May 16, 1958 7 Sheets-Sheet 1 INVEN TOR.

BY Paul H. Koch AT TORNEY Nev. 29, 1960 KOCH 2,962,005

FORCED FLOW VAPOR GENERATING UNIT Filed May 16, 1958 7 Sheets-Sheet 2/1so I INVENTOR.

BY Paul H .Koc h mam,-

ATTORNEY Nov. 29, 1960 P. H. KOCH FORCED FLOW VAPOR GENERATING UNIT 7Sheets-Sheet 3 Filed May 16, 1958 ATTORNEY NOV. 29, 1960 p, KOCH FORCEDFLOW VAPOR GENERATING UNIT '7 Sheets-Sheet 4 Filed May 16, 1958 FIG. 4

INVENTOR.

. Paul H. Koch BY wow/W ATTORNEY 7 sheets sheet 5 II I P. H. KOCH FORCEDFLOW VAPOR GENERATING UNIT FIG. 5

Nov. 29, 1960 Filed May 16, 1958 H 2 I 9 1 A 2 A III 1 1 6 w w 1 M m 2m. w 1 9/ V 1 l NOV. 29, 1960 KOCH 2,962,005

FORCED FLOW VAPOR GENERATING UNIT Filed May 16, 1958 7 Sheets-Sheet 6FIG.6

I'M Hwl-l W il i l -j IN V EN TOR.

Paul H. Koch AT TORNEY Nov. 29, 1960 P. H. KOCH FORCED FLOW VAPORGENERATING UNIT 7 Sheets-Sheet 7 Filed May 16, 1958 INVENTOR.

Paul H. Koch ATTORNEY FORCED FLUW VAPOR GENERATING UNIT Paul H. Koch,East Orange, N.J., assignor to The Babcock & Wilcox Company, New York,N.Y., a corporation of New Jersey Fiied May 16, 1958, Ser. No. 735,819

13 Claims. (31. 122-47s This invention relates to the construction andoperation of a forced flow fluid heating unit and more particularly toimprovements in the construction and operation of a forced circulationone-through vapor generating and superheating unit.

The general object of the present invention is the pro vision of acommercial size forced circulation oncethrough vapor generating andsuperheating unit adapted to produce superheated vapor from avaporizable fluid over a wide range of high pressures and temperatureswithout use of tempering equipment and characterized by its adaptabilityfor use at capacities commensurate with that of the prime mover served,operability with available commercial fuels at high combustionefiiciencies, and rapid response to load changes.

A further and more specific object of the invention is the provision ofa steam generating unit of the character described so constructed andarranged as to require a minimum of expensive structural supportingmembers; to assure an optimum distribution of fluid to all fluid flowpaths; to assure an optimum relation of fluid velocity within the tubesto heat input into the tube walls to effect adequate cooling of the tubewalls to a safe temperature; to provide a division of the fluid heatingsurface between the radiant and convection heated sections of the unitwhereby the water heating surface is mainly confined to the boundarywalls of the furnace chamber and a substantial portion of thesuperheating of the fluid is accomplished in the furnace; and to providesuperheating and reheating of the fluid in tube banks disposed inparallel convection gas passes of the unit.

The various features of novelty which characterize my invention arepointed out with particularity in the claims annexed to and forming apart of this specification. For a better understanding of the invention,its operating advantages and specific objects attained by its use,reference should be had to the accompanying drawings and descriptivematter in which I have illustrated and described a preferred embodimentof my invention.

Of the drawings:

Fig. l is a partially diagrammatic sectional elevation of a forcedcirculation once-through steam generating unit constructed and operablein accordance with the invention;

Fig. 2 is a plan section taken along the line 2-2 of Fig. 1

Fig. 3 is a plan section taken along the line 3-3 of Fig. 1;

Fig. 4 is a plan section taken along the line 44 of Fig. 1;

Fig. 5 is a partly diagrammatic plan section, one half of which ispartly broken away to show the secondary superheater supply tubes andupper headers, taken along the line 5-5 of Fig. 1;

Fig. 6 is a sectional elevation taken along the line 6-6 of Fig. 1;

Fig. 7 is a sectional elevation similar to Fig. 1 showice ing adiagrammatic representation of fluid flow paths in a side wall of thefurnace; and

Fig. 8 is a sectional elevation taken along the line 8-8 of Fig. 7.

In the drawings the invention has been illustrated as embodied in atop-supported forced flow once-through steam generating unit intendedfor central station use.

The particular unit illustrated is designed on oil and gas firing for amaximum continuous steam output of 1,63 8,- 000 pounds of steam per hourat a pressure of 2450 p.s.i'.g. and a total temperature of 1050" F. atthe superheater outlet, based on feed water being supplied at a pressureof 3070 p.s.i.g. and a temperature of 536 F-.; and a maximum continuoussteam output of 1,339,000 pounds steam per hour at a pressure of 533p.s.i.g. and a total temperature of 1000" F. at the reheater outlet.While the fluid heating unit construction illustrated and hereinafterdescribed is specifically designed and particularly adapted fortheproduction of superheated steam at pressures and temperatures belowthe critical pressure of 3206 p.s.i. and the critical temperature of 705F., it will be understood that the fluid heating unit illustrated may beadapted for operation at temperatures in excess of critical pressuresand temperatures.

The main portions of the unit illustrated include an upright furnacechamber 10 of substantially rectangular horizontal cross-section definedby front 12, rear 14, side 16 walls and a roof 18 and having a gasoutlet 20 at its upper end opening to a horizontally extending gas.

pass 22 of rectangular vertical cross-section formed by extensions ofthe furnace roof 18 and side walls 16 and a floor 24. The gas pass 22communicates at its rear end with the upper end of an upright gaspassage 24 of rectangular horizontal cross-section defined by a front.

wall 26, a rear wall 28, side walls 30, and a roof 32. The furnace 10 isdivided into a pair of compartments 34, 36 by a vertical partition wall38, each compartment opening at its upper end to the gas outlet 20. Thelower portions of the front and rear Walls of the furnace slope inwardlyand downwardly and cooperate with the furnace side walls to form ahopper 4t) and a rectangular throat passage 42 for discharging ash intoan ash pit, not shown. A secondary superheater 44 is disposed in. partin the upper portion of the furnace chamber 10 adjacent the gas outlet20 thereof, with the remainder occupying the furnace end of the gas pass22. The portion of the gas pass 22 downstream of the secondarysuperheater 44 is divided into parallel heating gas passes or' sections46 and 48 by a vertical baffle 50; and the upright gas passage 24 isdivided into parallel heating passes or sections 52 and 54 by a verticalbaffle 56, the passes 52 and 54 being continuations of passes 46 and 48,respectively. The gas pass 52 is occupied by a convection primarysuperheater 58, the gas pass 46 by an intermediate convection primarysuperheater 60, the gas pass. 54 by a primary reheater 62, and the gaspass 48 by a secondary reheater 64. Both of the gas passes 54, 52 areoccupied by an economizer 66 disposed downstream gas-wise of the primarysuperheater 58 and the reheater. 62. The heating gases from the gaspasses 52 and 54 respectively flow to ducts 67 and 69 from which thegases discharge into a common duct leading to an airheater, notshown.The proportioning of the gas flow between the passes 46, 52 and 48, 54is controlled by sets of dampers 71 and 73 in the ducts 67 and 69. Fromthe airheater the gases pass to an induced draft fan, and then to astack.

The vapor generator setting is top-supported by structural steel membersincluding upright members 61 and cross beams 63 from which hangers 65,of which only a few are illustrated, support all walls. I

The lower portion of the compartments 34, 36 of the furnace are fired byhorizontally extending burners 68 arranged to direct fuel and air inmixing relationship into the compartments through corresponding burnerports in the boundary walls of the furnace. The front, rear and sidewalls of the furnace each include two vertically spaced rows of burners,each row having two burners symmetrically arranged at opposite sides ofthe vertical centerline of the wall. Preheated air is supplied to theburners by a forced draft fan, not shown, which passes air underpressure through the airheater and a duct 70 to a vertically extendingwindbox 75 enclosing the burners 68 and the lower portion of theboundary walls of the furnace 10.

Feedwater at a pressure of 3070 p.s.i.g. is supplied by a feed pump, notshown, to the economizer 66 wherein it is partially heated. Theeconomizer comprises two sections of horizontally arrangedmultiple-looped nested return bend tubes disposed across the path ofheating gas flow and connected at their opposite ends to outlet andinlet headers '72 and 74 disposed on the centerline of the baflle wall56 and extending normal to the front and rear walls 26 and 28. From theouter header 72 the fluid flows through a downcomer 76 and supply tubes77 to the inlet headers for the fluid heating tubes lining the front,rear and side walls of the furnace 10, as shown in Fig. 1. p

The front, rear and side walls of the furnace 10 and the side walls ofthe gas pass 22 are formed by insulation covered metallic casing linedby fluid heating tubes secured thereto. Each of the boundary walls ofthe furnace 10 is lined by a row of vertically extending parallel tubesarranged in groups to form coplanar radiant heat absorbing tubularpanels extending between a corresponding number of horizontally arrangedupper and lower headers, the front wall 12 having a row of tubes 80forming tubular panels extending between upper and lower headers 82 and84, the rear wall 14 having a row of tubes '87 forming tubular panelsextending between upper and lower headers 86 and 88, and each side wall16 having a row of tubes 90 forming tubular panels extending betweenupper and lower headers 92 and 94. The tubes 90 also line the portion ofthe side walls of the gas pass 22 opposite the secondary superheater 44.The rear wall tubes 87 have their upper portions bent inwardly andupwardly to form a nose arch 96; then rearwardly and upwardly to formthe floor 24 of the gas pass 22; and then vertically for connection tothe headers 86 and to form a part of a screen 98 disposed downstreamgaswise of the intermediate primary superheater 60 and reheater section64 and at the rear end of the gas pass 22. Intermediate portions of someof the tubes of the front, rear and side walls of the furnace aresuitably bent to form the openings or ports for the burners 68. Thefurnace 10 has its corners beveled to promote heat absorption in thefluid heating tubes thereat, these tubes constituting the end tubes ofthe front and rear walls of the furnace.

In accordance with the present invention, the furnace boundary wallfluid heating surface is so proportioned and arranged that thedistribution of flow to all fluid flow paths is at an optimum; that themaximum temperature difierential between adjacent tubes is below apredetermined critical limit, thereby maintaining difierential expansions in the walls within safe limits; that fluid flow unbalances inthe tubes are minimized; that the tube surfaces in different zones ofheat intensity in the furnace are sufficient in quantity to carry awaythe heat at a rate adequate to prevent overheating of the tubes; andthat the tubes are of suflicient inside diameter along their lengths toprovide adequate fluid circulation velocities. Accordingly, each of thepanel fluid supply headers 84, 88, 94 is connected to the downcomer 76by one of the supply tubes 77. Each supply tube 77 is provided with aflow resistor 97, diagrammatically illustrated in Fig. l, at a pointwhere it joins the downcomer 76. These resistors impose a resistance towater flow which has a proportioning and equalizing effect on the amountof water entering each panel. The size of the flow resistors may bevaried for different panels, depending on their length, arrangement andheat absorption. The flow resistors are of predetermined size toregulate the amount of water flowing to each panel in accordance withthese variables. For the sake of clarity, Figs. 7 and 8 diagrammaticallyshow the flow path of the vaporizable fluid to, through and from some ofthe tubes of one of the tube panels of one of the side walls 16, thefluid flow path through the other tube panels of this wall and of thetube panels of the other side wall, the front wall 12 and the rear wall14 being substantially similar. Each side wall includes tube panels A Aand A Tube panel A comprises a group of tubes A arranged in equal numberon opposite sides of the vertical centerline of the panel A and inparallel relationship, with each tube 90A having, as clearly illustratedfor the panel A an upflow leg portion B extending in the furnace belowthe level of the upper end of the hopper 40, upflow and downflow legportions C extending between the level of the upper end of the hopperand the upper end of the windbox 75, and an upflow leg portion Dextending in the furnace above the level of the upper end of thewindbox. Since the tube lengths in the burner zone are exposed to gasesof higher heat intensity than those above and below the burner zone,their total absorption is highest and the quantity of heating surfacepresented by the tube lengths in the burner zone and the velocity of thefluid flowing through these tube lengths must be greater than that aboveand below the burner zone to carry away the heat at a rate sufiicient toprevent overheating of the tubes. Thus the upflow legs B of the tubes90A below the upper end of the hopper 40 are spaced about a tubediameter apart and are of a relatively small inside diameter. Theportions C of the tubes 90A extending in the burner zone between theupper end of the hopper 40 and the upper end of the windbox 75 are ofthe same inside diameter as the upflow legs B. The tube portions C ofeach of the tubes 90A consists of an initial upflow leg C, on one sideof the centerline of the panel A forming a vertical continuation of atube leg B, a downflow leg C and a final upflow leg C on the oppositeside of the centerline and spaced therefrom a distance about the same asthe distance of the leg C, from the adjacent end of the tube panel A Theupflow legs C are spaced about one tube diameter apart. The inlet endsof the upflow legs C of the tubes 90A disposed on one side of thecenterline of the panel A, are connected to the discharge ends of thetube legs B on the same side of the centerline; and the discharge endsof these upflow legs C are connected to the inlet ends of the upflowlegs C disposed on the opposite side of the centerline by the downflowlegs C which extend downwardly and laterally within the windbox 75, withthe legs C disposed between the legs C on the opposite side of thecenterline and contacting the legs C throughout the height of the burnerzone. Each tube of the panel A is formed and routed similar to those ofthe panel A the discharge ends of the initial upflow legs C of half ofthe tubes disposed on one side of the centerline of the panel A beingconnected to the inlet ends of the final upflow legs C disposed betweenthe initial upflow legs C of the other half of the tubes on the sameside of the centerline by downflow legs C extending downwardly andlaterally within the windbox 75. The same pattern is repeated for thetubes on the other side of the centerline of the panel A The tubes ofthe panel A in the burner zone are routed and formed in substantiallythe same manner as those of the panel A The tube lengths D of the sidewall panels above the windbox 75 are connected at their opposite ends tothe discharge ends of the final upflow legs C of the tubes in the burnerzone and to the upper headers 92, are spaced a tube diameter apart, areof a greater inside diameter than the tube lengths in the burner zone tominimize the fluid flow unbalances that may result from the relativelyhigh pres: sure drop of the fluid in flowing through the tube legs inthe hopper and burner zone; and are of suflicient diameter to providethe fluid velocity necessary to prevent overheating.

By way of example, and not of limitation, the furnace wall tube portionsbelow the burner zone are OD. x .391" ID. on 1%" centerlines; the tubeportions in the burner zone are .73" OD. x .391 ID. and substantiallytangent to each other; and the tube portions above the burner zone areOD. x .54 ID. on 1 /2 centerlines.

The outlet headers 82, 86 and 92 of the tube panels of the furnacefront, rear and side walls are connected for series flow of thevapor-liquid mixtures generated in the tube panels to a header 1% bytubular connectors 101, as shown in Fig. 5. The header 100 constitutesthe leg of a horizontally arranged T-shaped header having itscross-portion 1110A extending parallel to the front wall 12 and its legportion 1% in the plane of the centerline of the furnace 1d. Thevapor-liquid mixtures are mixed in passing through the T-shaped headerso that the enthalpy, and thereby the temperature, will be substantiallyuniform upon discharge therefrom. The header 100A is connected for flowof the vapor-liquid mixtures to a horizontally arranged fluiddistribution header 102 by a row of tubes 104 forming the roof of thefurnace and the gas pass 22.

The header 1112 is arranged to supply fluid to the tubes forming thebaflle walls of the gas pass 22 and the upright gas passage 24 and totubes lining the side walls of the gas pass 22 and the boundary walls ofthe gas passage 24. The portion of each of side walls of the gas pass 22downstream of the secondary superheater 44 is lined by a row ofvertically extending closely spaced parallel tubes 103 arranged ingroups to form tubular panels extending between a corresponding numberof horizontally arranged upper headers 106 and a horizontally extendingcommon lower header 108 disposed between the rear wall 1198 and thefront wall 26, with the headers 106 being connected to the header 102 bytubes 110 and the header 103 being connected at one end to a header112A. As shown in Fig. 3, the header 112A constitutes one leg of acontinuous horizontally arranged collecting header 112 disposed alongthe periphery of the gas passage 24 at a position intermediate theeconomizer 66 and the primary superheater 58. The lower portions of thetubes 103 cooperate with the rear wall 14, front wall 26 and a floor 114to form an idle compartment 116. The baflie wall 50 is formed by a rowof vertically extending closely spaced parallel tubes 11% arranged ingroups to form tubular panels extending between a corresponding numberof horizontally arranged upper headers 120 and. a horizontally extendingcommon lower header 122 disposed in the compartment 115, with theheaders 120 being connected to the header 1112 by tubes 124 and theheader 122 connected to the header 112A by tubes 126.

The front wall 26 of the gas passage 24 is formed by a row of verticallyextending spaced parallel tubes 128 having their intertube spaces closedby metallic webs; their upper ends connected to the header 1112; lowerends connected to the header 112A; and their upper portions bent toform, along with the upper portions of the tubes 87, the screen 98. Theroof 32 is formed by and the rear wall 28 is lined by a row of upwardlyextending closely spaced parallel tubes 1% having their upper endsconnected to the header 1112 and their lower ends to a leg 11213 of theheader 112. Each side wall 30 is lined by a row of tubes 132 arranged ingroups to form coplanar tubular panels extending between a correspondingnumber of upper headers 134 and a leg 112C of the header 112, with theupper headers 134 being connected to the header 102 by tubes 136. Thebafllle wall 56 is formed in part by a row of vertically extendingclosely spaced parallel tubes 13% arranged in groups to form coplanartubular panels extending between a corresponding number of horizontallyarranged upper headers and a common horizontally extending lower header142, with the upper headers being connected to the header 102 by tubesand the lower header 142 having its opposite ends connected to theheaders 112A and 112B, respectively. The remainder of the baflle 56 isformed by a metallic wall 56A suitably secured to the header 142 and theeconomizer headers 72 and 74 and extending downwardly from the bottom ofthe header 142 to the ducts 71 and 73. Thus the header 1612 is connectedfor parallel downflow of fluid to tubes of the side and baffle walls ofthe gas pass 22 and the boundary walls of the upright gas passage andthe header 112 is connected to receive the fluid discharging from all ofthe these tubes. The vapor-liquid mixtures flowing through the header112 are mixed therein so that the enthalpy, and thereby the temperature,will be substantially uniform upon discharge therefrom. The fluids thusmixed pass to the primary superheater 58.

The primary superheater 58 comprises three groups of horizontallydisposed nested multi-looped tubes arranged in laterally spaced panelsserially connected to define parallel flow paths for fluid flow betweenthe headers 112A and 11213 and a transverse external outlet header 144in counterflow heat transfer relation to the gases flowing through theparallel gas pass 52. From the header 144 the partly superheated vaporpasses to the intermediate primary superheater 60 which comprises agroup of pendently supported vertically disposed nested multiple-loopedtubes arranged in laterally spaced panels to define parallel flow pathsfor vapor flow between the header 144 and a transverse header 14$disposed in the compartment 116, with the tubes being arranged so thatvapor flows first in counterflow heat transfer relation to the gases andthen in parallel flow heat transfer relation.

The additionally superheated vapor then flows through a downcomer andsupply tubes 152 to the final primary vapor superheating tubes formingthe partition wall 38 of the furnace.

The partition wall 38 extends normal to the front and rear walls 12 and14 of the furnace 10 and is formed by two coplanar tubular panels E andF, each panel being formed by final primary vapor superheating tubes 154contacting each other along their lengths and extending verticallythroughout the height of the furnace. The panel E extends between ahorizontally arranged upper outlet header 155 and a pair of lowerheaders 156 which are disposed parallel to and outside of the front wallof the hopper 40. As shown in Fig. 5, the header 155 constitutes one legof a horizontally arranged cross-shaped header and extends subjacent andin the same vertical plane as the header 1%, the other leg 155Aextending normal to the leg 155 and parallel to the front wall 12. Thepanel F extends between the header 15S and a lower header 158 which isdisposed parallel to and outside of the rear wall of the hopper it Thepanel B is spaced from the front wall 12 and the panel F is spaced aslight distance from the nose arch 96 and from the panel E to provideopenings 16th for the flow of gases between the compartments 34, 36 ofthe furnace. The headers 156 and 158 are connected to the clowncomer1511 by the tubes 152 to provide parallel upflow of vapor through thepanels E and F. The vapor thus further superheated passes from theheader 155 to the header 155A, and then through tubes 162 to thesecondary superheater 44.

The secondary superheater comprises two groups 44A and 44B of tubes.Group 44A includes horizontally spaced pendantly supported radiant heatabsorbing tube platens arranged in vertical planes in the direction ofgas flow, with each platen having a multiplicity of nested return bendtubes connected at their opposite ends to a horizontally arranged inletheader 164 and a horizontally extending inlet-outlet header 166, withthe inlet headers 164 being connected to the header 155A by the tubes162..

Group 44B comprises pendantly supported vertically dis posed nestedmultiple-looped tubes arranged in laterally spaced panels to defineparallel flow paths for vapor flow between the header 166 and atransverse header 170 disposed in the compartment 116, with the tubesbeing arranged so that the vapor flows first in parallel flow heattransfer relation with the gases flowing through the gas pass 22 andthen in counterflow heat transfer relation. The vapor receives its finalsuperheating in this group of tubes and is discharged to outlet header170 from which it passes through a conduit 172 to the high pressurestage of a vapor turbine, not shown.

The primary reheater 62 comprises horizontally extending nestedmultiple-looped tubes arranged substantially similar to the tubes of theprimary superheater and in contrafiow relation with the heating gasesand having their opposite ends connected to a lower inlet header 17d andan upper transverse outlet header 176, with the inlet header 174receiving partially expanded vapor from the turbine. From the header 176the partly reheated vapor passes to the secondary reheater 48 whichcomprises vertically disposed nested multiple-looped tubes arrangedsubstantially similar to the tubes of the intermediate primarysuperheater 46 and having their opposite ends connected to the header176 and a transverse outlet header 178 disposed in the compartment 116.The finally reheated vapor then passes from the header 178 through aconduit 179 to the turbine for final expansion.

Thus in operation the high pressure fluid supplied by the feed pumppasses through the economizer 66; then flows in parallel through theradiant heat absorbing tube panels of the front, rear and side walls ofthe furnace; then through the tubes 104 forming the roof of the furnaceand the gas pass 22; then in parallel through the convection heatabsorbing fluid heating tubes of the side and baffle walls of the gaspass 22 and the boundary and baflle walls of the gas passage 24; thensuccessively passes through the primary superheater vapor superheatingtubes 58, the intermediate primary vapor superheating tubes 69, theprimary final vapor superheating tubes forming the division wall 38 ofthe furnace 10 and the secondary vapor superheating tubes 44; and thenflows to the high pressure stage of the turbine. Partially expandedsteam from the turbine successively passes through the primary vaporreheating tubes 62 and the secondary vapor reheating tubes 64, fromwhich it returns to the turbine for final expansion.

Combustion air and fuel are supplied through the burner ports to thelower portion of each of the compartments 34, 36. The resulting heatinggases flow upwardly through the compartments 34, 36 and over the radiantheating absorbing portion 44A of the secondary superheater to the gasinlet of the gas pass 22; then flow horizontally through the furnace endof the gas pass 22 in contact with the convection heat absorbing portion44B of the secondary superheater; and then divide into parallel streams,with one stream successively passing through the gas section 46 and thegas section 52 in contact with the intermediate primary vaporsuperheating tubes 60 and the primary vapor superheating tubes 58, andthe other stream successively passing through the gas section 48 and thegas section 54 in contact with the secondary vapor reheating tubes 64and the primary vapor reheating tubes 62. The proportioning of the gasflow between the gas sections 46, 52 and the gas sections 48, 54 iscontrolled by the sets of dampers 71 and 73.

The superheating and reheating surfaces are propor tioned and arrangedto provide the required final or ou let steam temperatures at full steamload. The proportion of the heating gases flowing through the gassections 48, 54 and 46, 52 are respectively increased and decreased bymeans of the dampers 73 and 71 as the rate of steam generation decreasesto hold the reheater outlet steam temperature constant over a wide rangeof steam loads, while the final superheater outlet steam temperature ismaintained constant by controlling the firing rate of the t 8 burners.The vapor generating and superheating surfaces are proportioned andarranged so that the portion of the heated fluid circuit in which thetransition of the water from a liquid to a vapor condition occurs willalways be located in the relatively low temperature primary superheater58 throughout the operating range.

While in accordance with the provisions of the statutes illustrated anddescribed herein a specific form of the invention now known to me, thoseskilled in the art will understand that changes may be made in the formof the apparatus disclosed without departing from the spirit of theinvention covered by my claims, and that certain features of theinvention may sometimes be used to advantage without a corresponding useof other features.

What is claimed is:

1. A once-through forced circulation vapor generator comprising wallsincluding radiant heat absorbing fluid heating tubes in the form ofpanels arranged for parallel flow of fluid therethrough defining anupright furnace chamber having a heating gas outlet, means forming a gaspass serially connected to said gas outlet, a bank of vapor superheatingtubes positioned in said gas pass in the path of gas flow leaving saidfurnace chamber, means including a row of vapor superheating tubesdividing said furnace chamber into a pair of gas flow compartments eachopening to said gas outlet, means for burning fuel in said furnacechamber, means for supplying a vaporizable fluid to said radiant heatabsorbing fluid heating tubes under a substantial pressure, and meansfor interconnecting said fluid heating and vapor superheating tubes toprovide a serial flow of fluid successively through said radiant heatabsorbing fluid heating tubes, vapor superheating tubes dividing saidfurnace chamber, and bank of vapor superheating tubes.

2. A once-through forced circulation vapor generator comprising wallsincluding upwardly extending radiant heat absorbing fluid heating tubesin the form of panels arranged for parallel flow of fluid therethroughdefining an upright furnace chamber having a heating gas outlet at itsupper end and its corners beveled to promote heat absorption in thefluid heating tubes thereat, means forming a gas pass opening to saidgas outlet, a bank of vapor superheating tubes positioned in said gaspass in the path of gas flow leaving said furnace chamber, meansincluding a row of vapor superheating tubes dividing said furnacechamber into a pair of intercommunicating gas flow compartments eachopening at its upper end to said gas outlet, means for burning fuel inthe lower portion of each of the compartments of said furnace chamber,means for supplying a vaporizable fluid to each of said tube panelsunder a substantial pressure, and means for interconnecting said fluidheating and vapor superheating tubes to provide a serial flow of fluidsuccessively through said radiant heat absorbing fluid heating tubes,vapor superheating tubes dividing said furnace chamber, and bank ofvapor superheating tubes.

3. A once-through forced circulation vapor generator comprising wallsincluding radiant heat absorbing fluid heating tubes in the form ofpanels arranged for parallel flow of fluid therethrough defining anupright furnace chamber having a heating gas outlet, means forming a gaspass serially connected to said gas outlet, a bank of vapor superheatingtubes positioned in said gas pass in the path of gas flow leaving saidfurnace chamber, means including a row of vapor superheating tubesdividing said furnace chamber into a pair of gas flow compartments eachopening to said gas outlet, means for burning fuel in said furnacechamber, a plurality of tubular conduits each supplying fluid to one ofsaid tube panels, means for supplying a vaporizable fluid to each ofsaid tubular conduits under a substantial pressure, a flow resistor ineach of said tubular conduits proportioned to regulate the amount offluid entering each of said tube panels, and means for interconnectingsaid fluid heating and vapor superheating tubes to provide a serial flowof fluid successively through said radiant heat absorbing fluid heatingtubes, vapor superheating tubes dividing said furnace chamber, and bankof vapor superheating tubes.

4. A-once-through forced circulation vapor generator comprising wallsincluding upwardly extending radiant heat absorbing fluid heating tubesin the form of panels arranged for parallel flow of fluid therethroughdefining an upright furnace chamber having a heating gas outlet, meansforming a gas pass serially connected to said gas outlet, a bank ofsecondary vapor superheating tubes positioned in said gas pass in thepath of gas flow leaving said furnace chamber, a bank of primary vaporsuperheating tubes positioned downstream gas-wise of said secondaryvapor superheating tubes, means including a row of vapor superheatingtubes dividing said furnace chamber into a pair of gas flow compartmentseach opening to said gas outlet, means for burning fuel in said furnacechamber, means for supplying a vaporizable fluid to each of said tubepanels under a substantialpressure, and means for interconnecting saidfluid heating and vapor superheating tubes to provide a serial flow offluid successively through said radiant heat absorbing fluid heatingtubes, bank of primary vapor superheating tubes, vapor superheatingtubes dividing said furnace chamber, and bank of secondary vaporsuperheating tubes.

5. A once-through forced circulation vapor generator comprising wallsincluding upwardly extending radiant heat absorbing fluid heating tubesin the form of panels arranged for parallel flow of fluid therethroughdefining an upright furnace chamber having a heating gas outlet, meansforming a gas pass serially connected to said gas outlet, a bank ofsecondary vapor superheating tubes positioned in said gas pass acrossthe full width thereofin the path of gas flow leaving said furnacechamber, means dividing said gas pass downstream of said secondary vaporsuperheating tubes into a pair of parallel flow gas sections, a bank ofprimary vapor superheating tubes positioned in said gas pass in one ofthe parallel gas flow sections thereof, a bank of vapor reheating tubespositioned in said gas pass in the other of the parallel gas flowsections thereof, means including a row of vapor superheating-tubesdividing said furnace chamber into a pair of gas flow compartments eachopening to said gas outlet, damper means arranged to proportion theheating gas flow through said parallel gas flow sections, means forburning fuel in said furnace chamber, means for supplying a vaporizablefluid to each of said tube panels under a substantial pressure, andmeans for interconnecting said fluid heating and vapor superheatingtubes to provide a serial flow of fluid successively through saidradiant heat absorbing fluid heating tubes, bank of primary vaporsuperheating tubes, vapor superheating tubes dividing said furnacechamber, and bank of secondary vapor superheating tubes.

6. A once-through forced circulation vapor generator comprising wallsincluding upwardly extending radiant heat absorbing fluid heating tubesin the form of panels arranged for parallel flow of fluid therethroughdefining an upright furnace chamber having a heating gas outlet, meansincluding convection heat absorbing fluid heating tubes forming a gaspass serially connected to said gas outlet, a bank of secondary vaporsuperheating tubes positioned in said gas pass in the path of gas flowleaving said furnace chamber, a bank of primary vapor superheating tubespositioned downstream gas-wise of said secondary vapor superheatingtubes, means including a row of vapor superheating tubes dividing saidfurnace chamber into a pair of gas flow compartments each opening tosaid gas outlet, means for burning fuel in the lower portion of each ofthe compartments of said furnace chamber, means for supplying avaporizable fluid to each of said tube panels under a substantialpressure, and means for interconnecting said fluid heating and vaporsuperheating tubes to provide a serial flow of fluid successivelythrough said radiant heat absorbing fluid heating tubes, convection 10heat absorbing fluid heating tubes, bank of primary vapor superheatingtubes, vapor superheating tubes dividing said furnace chamber, and bankof secondary vapor superheating tubes.

7. A once-through forced circulation vapor generator comprising wallsincluding upwardly extending radiant heat absorbing fluid heating tubesin the form of panels arranged for parallel flow of fluid therethroughdefining an upright furnace chamber having a heating gas outlet at itsupper end and its corners beveled to promote heat absorption in thefluid heating tubes thereat, means including convection heat absorbingfluid heating tubes forming a gas pass serially connected to said gasoutlet, a bank of secondary vapor super-heating tubes positioned in saidgas pass in the path of gas flow leaving said furnace chamber, meansincluding convection heat absorbing fluid heating tubes dividing saidgas pass downstream of said secondary vapor superheating tubes into apair of parallel flow gas sections, a bank of primary vapor superheatingtubes positioned in said gas pass in one of t the parallel gas flowsections thereof, a bank of vapor reheating tubes positioned in said gaspass in the other of the parallel gas flow sections thereof, meansincluding a row of vapor superheating tubes dividing said furnacechamber into a pair of gas flow compartments each opening to said gasoutlet, damper means arranged to proportion the heating gas flow throughsaid parallel gas flow sections, means for burning fuel in the lowerportion of each of the compartments of said furnace chamber, means forsupplying a vaporizable fluid to each of said tube panels under asubstantial pressure, and means for interconnecting said fluid heatingand vapor super-heating tubes to provide a serial flow of fluidsuccessively through said radiant heat absorbing fluid heating tubes,convection heat absorbing fluid heating tubes, bank of primary vaporsuperheating tubes, vapor superheating tubes dividing said furnacechamber, and bank of secondary vapor superheating tubes.

8. A once-through forced circulation vapor generator comprising wallsincluding upwardly extending radiant heat absorbing fluid heating tubesin the form of panels arranged for parallel flow of fluid therethroughdefining an upright furnace chamber having a heating gas outlet at itsupper end, means including convection heat absorbing fluid heating tubesforming a horizontally extending gas pass opening at one end to said gasoutlet, a bank of secondary vapor superheating tubes positioned in saidgas pass in the path of gas flow leaving said furnace chamber, meansincluding convection heat absorbing fluid heating tubes forming anupright gas passage laterally adjacent and opening to the opposite endof said gas pass, means including convection heat absorbing fluidheating tubes dividing said upright gas passage and said gas passdownstream of said secondary vapor superheating tubes into a pair ofparallel flow gas sections, a bank of primary vapor superheating tubespositioned in said upright gas passage in one of the parallel gas flowsections thereof, an intermediate bank of. primary vapor superheatingtubes positioned in said gas pass in said one parallel gas flow sectionintermediate said banks of primary and secondary vapor superheatingtubes, a bank of primary vapor reheating tubes in said upright gaspassage in the other of the parallel gas flow sections thereof, a bankof secondary vapor reheating tubes positioned in said gas pass in saidotherparallel-gas flow section and connected for series flow of vaporfrom said bank of primary vapor reheating tubes, means including a rowof final primary vapor superheating tubes dividing said furnace chamberinto a pair of intercommunicating gas flow compartments each opening atits upper end to said gas outlet, damper means arranged to proportionthe heating gas flow through said parallel gas flow sections, means forburning fuel in the lower portion of each of the compartments of saidfurnace chamber, means for supplying a vaporizable fluid to each of saidtube panels under a Substantial pressure, and means for interconnectingsaid fluid heating and vapor superheating tubes to provide a serial flowof fluid successively through said radiant heat absorbing fluid heatingtubes, convection heat absorbing fluid heating tubes, bank of primaryvapor superheating tubes intermediate bank of primary vapor superheatingtubes, vapor superheating tubes dividing said furnace chamber, and bankof secondary vapor superheating tubes.

9. A once-through forced circulation vapor generator comprising wallsincluding upwardly extending radiant heat absorbing fluid heating tubesin the form of panels arranged for parallel flow of fluid therethroughdefining an upright furnace chamber having a heating gas outlet at itsupper end, means including convection heat absorbing fluid heating tubesforming a horizontally extending gas pass opening at one end to said gasoutlet, a bank of secondary vapor superheating tubes positioned in saidgas pass in the path of gas flow leaving said furnace chamber, meansincluding convection heat absorbing fluid heating tubes forming anupright gas passage laterally adjacent and opening to the opposite endof said gas pass, means including convection heat absorbing fluidheating tubes dividing said upright gas passage and said gas passdownstream of said secondary vapor superheating tubes into a pair ofparallel flow gas sections, a bank of primary vapor superheating tubespositioned in said upright gas passage in one of the parallel gas flowsections thereof, an intermediate bank of primary vapor superheatingtubes positioned in said gas pass in said one parallel gas flow sectionintermediate said banks of primary and secondary vapor superheatingtubes, a bank of primary vapor reheating tubes in said upright gaspassage in the other of the parallel gas flow sections thereof, a bankof secondary vapor reheating tubes positioned in said gas pass in saidother parallel gas flow section and connected for series flow of vaporfrom said bank of primary vapor reheating tubes, means including a rowof final primary vapor superheating tubes dividing said furnace chamberinto a pair of inter-communicating gas flow compartments each opening atits upper end to said gas outlet, damper means arranged to proportionthe heating gas flow through said parallel gas flow sections, means forburning fuel in the lower portion of each of the compartments of saidfurnace chamber, a plurality of tubular conduits each supplying fluid toone of said tube panels, means for supplying a vaporizable fluid to eachof said tubular conduits under a substantial pressure, a flow resistorin each of said tubular conduits proportioned to regulate the amount offluid entering each of said tube panels, and means for interconnectingsaid fluid heating and vapor superheating tubes to provide a serial flowof fluid successively through said radiant heat absorbing fluid heatingtubes, convection heat absorbing fluid heating tubes, bank of primaryvapor superheating tubes, intermediate bank of primary vaporsuperheating tubes, vapor superheating tubes dividing said furnacechamber, and bank of secondary vapor superheating tubes.

10. In a forced circulation fluid heating unit, walls defining a furnacechamber for the flow of heating gases, burner means supplying hightemperature heating gases to said chamber and establishing a gas flowzone intermediate the height of said chamber and in the vicinity of saidburner means of higher heat intensity than exists in the portions ofsaid chamber above and below said zone, at least one of said wallsincluding a plurality of laterally contiguous tubular panels arrangedfor parallel flow of fluid therethrough, each of said panels comprisinga group of upwardly extending tubes arranged for parallel flow of fluidtherethrough, each of said tubes of each panel including continuousinitial upflow legs extending below and throughout said zone of highheat intensity and second upflow legs extending throughout and abovesaid zone of high heat intensity, means for supplying a vaporizablefluid of substantially the same enthalpy in parallel flow relationdirectly from a common source to the lower inlet ends of said initialupflow legs of each of said panels, said initial upflow legs beingarranged in parallel spaced relation to provide intertube spaces, saidsecond upflow legs being disposed in the spaces between and contiguousto said initial upflow legs along the height of said Zone so that thenumber of tube legs presented to the gases in the zone of high heatintensity is double that below and above said zone, and downflow tubularmeans disposed externally of said one wall and arranged to connect theupper discharge ends of said initial upflow legs for series flow offluid to the lower inlet ends of said second upflow legs.

11. In a forced circulation fluid heating unit, walls defining a furnacechamber for the flow of heating gases, burner means supplying hightemperature heating gases to said chamber and establishing a gas flowzone intermediate the height of said chamber and in the vicinity of saidburner means of higher heat intensity than exists in the portions ofsaid chamber above and below said zone, at least one of said wallsincluding a plurality of upwardly extending laterally contiguous tubularpanels arranged for parallel flow of fluid therethrough, each of saidtubes of each panel including a continuous initial upflow leg extendingbelow and throughout said zone of high heat intensity and a secondupflow leg extending throughout and above said zone of high heatintensity, and means for supplying a vaporizable fluid of substantiallythe same enthalpy in parallel flow relation directly from a commonsource to the lower inlet ends of said initial upflow legs of each ofsaid panels, said initial upflow legs being arranged in parallel spacedrelation and having their upper discharge ends connected for series flowof fluid to the lower inlet ends of said second upflow legs by downfiowtube legs disposed externally of said one wall, said second upflow legsbeing disposed in the spaces between and contiguous to said upflow legsalong the height of said zone so that the number of tube legs presentedto the gases in the zone of high heat intensity is double that below andabove said zone.

12. In a forced circulation fluid heating unit, walls defining a furnacechamber for the flow of heating gases, burner means supplying hightemperature heating gases to said chamber and establishing a gas flowzone intermediate the height of said chamber and in the vicinity of saidburner means of higher heat intensity than exists in the portions ofsaid chamber above and below said zone, each of said walls including aplurality of upwardly extending coplanar laterally continguous tubularpanels arranged for parallel flow of fluid therethrough, each of saidpanels comprising a group of upwardly extending tubes arranged forparallel flow of fluid therethrough, each of said tubes of each panelincluding a continuous initial upflow leg extending below and throughoutsaid zone of high heat intensity and a second upflow leg extendingthroughout and above said zone of high heat intensity, and means forsupplying a vaporizable fluid of substantially the same enthalpy inparallel flow relation direction from a common source to the lower inletends of said initial upflow legs of each of said panels, said initialupflow legs being arranged in parallel spaced relation to provideintertube spaces and having their upper discharge ends connected forseries flow of fluid to the lower inlet ends of said second upflow legsby downflow tube legs disposed externally of said chamber, said secondupflow legs being disposed in the spaces between and contiguous to saidinitial upflow legs along the height of said zone so that the number oftube legs presented to the gases in the zone of high heat intensity isdouble that below and above said zone, the portions of said secondupflow legs above said zone having a greater inside diameter than theportions of said second upflow legs in said zone to minimize fluid flowunbalances in the tubes.

13. In a forced circulation fluid heating unit, walls defining a furnacechamber for the flow of heating gases, burner means supplying hightemperature heating gases to said chamber and establishing a gas flowzone intermediate the height of said chamber and in the vicinity of saidburner means of higher heat intensity than exists in the portions ofsaid chamber above and below said zone, each of said walls including aplurality of upwardly extending coplanar laterally contiguous tubularpanels arranged for parallel flow of fluid therethrough, each of saidpanels comprising a group of upwardly extending tubes arranged forparallel flow of fluid therethrough, each of said tubes of each panelincluding continuous initial upflow legs having their lower inlet endsconnected to a fluid distribution header and extending below andthroughout said zone of high heat intensity and second upflow legsextending throughout and above said zone of high heat intensity, atubular conduit connected to the fluid distribution header of eachpanel, means for supplying a vaporizable fluid of substantially the sameenthalpy in parallel flow relation directly from a common source to eachtubular conduit, and a flow resistor in each tubular conduitproportioned to regulate the amount of fluid entering each panel, saidinitial upflow legs being arranged in parallel spaced relation andhaving their upper discharge ends connected for series flow of fluid tothe lower inlet ends of said second upflow legs by downflow tube legsdisposed externally of said chamber, said second upflow legs beingdisposed in the spaces between and contiguous to said initial upflowlegs along the height of said zone so that the number of tube legspresented to the gases in the zone is double that below and above saidzone, the portions of said second upflow legs above said zone having agreater inside diameter than the portions of said second upflow legs insaid zone to minimize fluid flow unbalances in the tubes.

References Cited in the file of this patent FOREIGN PATENTS 857,965Germany Dec. 4, 1952 663,892 Great Britain Dec, 27, 1951 744,797 GreatBritain Feb. 15, 1956

